Biology subjects

Gehringer, M. M.

Publications and source records attributed to Gehringer, M. M..

8 recordsLinked to original sources

bioRxiv2026

Comparative study on chromatic acclimation in the two Synechococcus species WH8109 and RS9916

Marine Synechococcus cyanobacteria can modify their light-harvesting phycobilisome antennae in response to spectral changes through chromatic acclimation (CA). CA type IV (CA4) involves adjustment of the ratio of the blue-absorbing phycourobilin (PUB) to the green-absorbing phycoerythrobilin (PEB). Although CA4 is associated with a genomic island occurring in two configurations (CA4-A and CA4-B), some strains carrying this island, including Synechococcus sp. WH8109, have been reported to lack CA4 activity. Here, we investigated whether WH8109 undergoes CA4 under blue light (BL) and green light (GL) conditions, using the CA4-positive strain RS9916 as a reference. Whole-cell fluorescence, flow cytometry, isolated phycobilisome analysis, and sequencing of the CA4-B genomic island were used to assess pigment acclimation and identify potential genetic differences. WH8109 showed a stable PUB:PEB ratio of approximately 0.71 under BL and GL, with no detectable changes in PUB content or phycobilisome chromophore composition. In contrast, RS9916 exhibited clear CA4, with PUB:PEB ratios of 1.57 under BL and 0.72 under GL. Sequencing revealed no insertions, deletions, or other sequence anomalies in the WH8109 CA4-B genomic island compared to the public sequence. These results demonstrate that WH8109 does not undergo detectable CA4 under the conditions tested, despite possessing an intact CA4-B genomic island, highlighting a genotype-phenotype discrepancy that warrants further investigation.

microbiology↗

bioRxiv2024

Exploring the influence of atmospheric CO2 and O2 levels on the utility of nitrogen isotopes as proxy for biological N2 fixation

Biological N2 fixation (BNF) can be traced to the Archean, over 3 Bya. The nitrogen isotopic fractionation composition ({delta}15N) of sedimentary rocks is commonly used to reconstruct the presence of diazotrophic ecosystems in the past. While {delta}15N has been calibrated under modern environmental conditions; it has not under Archean conditions, when atmospheric pO2 was lower and pCO2 was higher than today. Here we explore {delta}15N signatures in the laboratory under three simulated atmospheres with (i) elevated CO2 and no O2, (ii) present day CO2 and O2 and (iii) elevated CO2 and present day O2, in marine and freshwater, heterocytous cyanobacteria. Additionally, we augment our data set with literature data to examine for more generalized dependencies of {delta}15N during BNF across the Archaea and Bacteria, including cyanobacteria, and habitats. We find a mean {varepsilon}-value of -1.38 {+/-} 0.95, for all bacteria, including cyanobacteria, across all tested conditions. The expanded data set reveal correlations of isotopic fractionation of BNF with CO2 concentrations, toxin production and light, although within 1 {per thousand}. Moreover, correlation showed significant dependency of the magnitude of {varepsilon} to species type, C/N ratios and toxin production in heterocytous cyanobacteria, albeit it within a small range (-1.44 {+/-} 0.89). We therefore conclude that {delta}15N is likely robust when applied to the Archean, stressing the strong cyanobacterial bias. Interestingly, the increased fractionation (lower {varepsilon}) observed in the toxin producing Nodularia and Nostoc spp. suggests a heretofore unknown role of toxins in modulating nitrogen isotopic signals that warrants further investigation. ImportanceNitrogen is an essential element of life on Earth, however, despite its abundance it is not biologically accessible. Biological nitrogen fixation is an essential process whereby microbes fix N2 into biologically usable NH3. During this process, the enzyme nitrogenase preferentially uses light 14N, resulting in 15N depleted biomass. This signature can be traced back in time in sediments on Earth, and possibly other planets. In this paper, we explore the influence of pO2 and pCO2 on this fractionation signal. We find the signal is stable, especially for the primary producers, cyanobacteria, with correlations to CO2, light and toxin producing status, within a small range. Unexpectedly, we identified higher fractionation signals in toxin producing Nodularia and Nostoc species, that offers insight into why some organisms produce these N-rich toxic secondary metabolites.

microbiology↗

bioRxiv2024

Early-branching cyanobacteria up-regulate superoxide dismutase activity under a simulated early Earth anoxic atmosphere.

The evolution of oxygenic photosynthesis during the Archean (4-2.5 Ga), required the presence of complementary reducing pathways to maintain the cellular redox balance. While the timing of the evolution of superoxide dismutases (SODs), enzymes that convert superoxide to hydrogen peroxide, within the Bacteria and Archaea is not resolved, SODs containing copper and zinc in the reaction centre (CuZnSOD) were the first SODs estimated to appear in photosynthetic cyanobacteria, [≥] 2.93 Ga. Here we analysed the SOD gene expression and activity in the deep branching strain, Pseudanabaena sp. PCC7367. It releases more O2 and exhibits significantly higher growth rates (p<0.001) and protein and glycogen contents (p<0.05) under anoxic conditions compared to control cultures grown under present oxygen rich atmospheres in low CO2 (LC) or high CO2 (HC), prompting the question as to whether this correlates to higher cellular SOD activity under anoxic Archean simulated conditions. Expression of sodB encoding an iron containing SOD (FeSOD) and sodC, encoding a CuZnSOD, strongly correlated with increased extracellular O2 levels (p<0.001), while transcription of sodA, encoding a manganese containing (MnSOD), correlated to SOD activity during the day (p=0.019), when medium O2 concentrations were the highest. Cytosolic SOD activity was significantly higher (p<0.001) in anoxic cultures, two hrs before nightfall compared to oxic growth conditions. Night-time combined sodABC transcription in stirred cultures was significantly reduced (p<0.05) under anoxic conditions at elevated CO2 levels, as were medium O2 levels (p[≤]0.001), when compared to cultures grown under present-day oxic conditions with low CO2. Total cytosolic SOD activity remained comparable, suggesting that the replacement rate of SOD is higher under modern-day conditions than on early Earth. Our data suggest that the early branching cyanobacterium Pseudanabaena sp. PCC7367 may have retained ancestral features permitting it to thrive in its ecological niche as a benthic mat in shallow water marine environments.

microbiology↗

bioRxiv2023

Expanding the toolbox for phycobiliprotein assembly: phycoerythrobilin biosynthesis in Synechocystis

Phycobiliproteins (PBPs) play a vital role in light harvesting by cyanobacteria, which enables efficient utilization of photon energy for oxygenic photosynthesis. The PBPs carry phycobilins, open-chain tetrapyrrole chromophores derived from heme. The structure and chromophore composition of PBPs is dependent on the organisms ecological niche. In cyanobacteria, these holo-proteins typically form large, macromolecular antenna complexes called phycobilisomes (PBSs). The PBS of Synechocystis sp. PCC 6803 (hereafter Synechocystis) consists of allophycocyanin (APC) and phycocyanin (PC), which exclusively harbor phycocyanobilin (PCB) as a chromophore. Investigations into heterologous PBP biosynthesis in E. coli have proven limiting with respect to PBP assembly and their functional characterization. Consequently, we wanted to engineer a platform for the investigation of heterologously produced PBPs, focusing on unusual, phycoerythrobilin (PEB)-containing light-harvesting proteins called phycoerythrins (PEs) in Synechocystis. As a first step, a gene encoding for the synthesis of the natural cyanobacterial chromophore, PEB, was introduced into Synechocystis. We provide spectroscopic evidence for heterologous PEB formation and show covalent attachment of PEB to the -subunit of PC, CpcA, by HPLC and LC-MS/MS analyses. Fluorescence microscopy and PBS isolation demonstrate a cellular dispersal of PBPs with modified phycobilin content. However, these modifications have minor effects on physiological responses, as demonstrated by growth rates, oxygen evolution, nutrient accumulation, and PBP content analyses. As a result, Synechocystis demonstrates the capacity to efficiently manage PEB biosynthesis and therefore reflects a promising platform for both biochemical and physiological investigations of foreign and unusual PEs.

synthetic biology↗

bioRxiv2021

Lack of Fe(II) transporters in basal Cyanobacteria complicates iron uptake in ferruginous Archean oceans.

Introductory paragraphCyanobacteria oxygenated Earths atmosphere during the Great Oxygenation Event (GOE) through oxygenic photosynthesis. Their high iron requirement was presumed met by high levels of Fe(II) in the anoxic Archean ocean. Here we show that most basal Cyanobacteria cannot synthesize the primary Fe(II) transporter, FeoB. Relaxed molecular clock analyses estimate the arrival of FeoB, as well as the Fe(III) transporters, cFTR1 and FutB, in the Cyanobacteria after the GOE. Furthermore Pseudanabaena sp. PCC7367, a basal marine, benthic strain grown under simulated Archean conditions, constitutively expressed cftr1, even after the addition of Fe(II). By utilizing gene expression studies under a simulated Archean atmosphere, as well as comparative genomics, phylogenetics and molecular clock analyses, this study identified a need to reappraise iron uptake in ancestral Cyanobacteria, as genetic profiling suggests that scavenging of siderophore bound Fe(III), rather than Fe(II), appears to have been the means of iron acquisition prior to the GOE.

evolutionary biology↗

bioRxiv2020

A low-cost automized anaerobic chamber for long-term growth experiments and sample handling

1The handling of oxygen sensitive samples and growth of obligate anaerobic organisms requires the stringent exclusion of oxygen, which is omnipresent in our normal atmospheric environment. Anaerobic workstations (aka. Glove boxes) enable the handling of oxygen sensitive samples during complex procedures, or the long-term incubation of anaerobic organisms. Depending on the application requirements, commercial workstations can cost up to 60.000 {euro}. Here we present the complete build instructions for a highly adaptive, Arduino based, anaerobic workstation for microbial cultivation and sample handling, with features normally found only in high cost commercial solutions. This build can automatically regulate humidity, H2 levels (as oxygen reductant), log the environmental data and purge the airlock. It is built as compact as possible to allow it to fit into regular growth chambers for full environmental control. In our experiments, oxygen levels during the continuous growth of oxygen producing cyanobacteria, stayed under 0.03 % for 21 days without needing user intervention. The modular Arduino controller allows for the easy incorporation of additional regulation parameters, such as CO2 concentration or air pressure. This paper provides researchers with a low cost, entry level workstation for anaerobic sample handling with the flexibility to match their specific experimental needs. Specifications table[please fill in right-hand column of the table below] O_TBL View this table: org.highwire.dtl.DTLVardef@18b371aorg.highwire.dtl.DTLVardef@cead94org.highwire.dtl.DTLVardef@e5dd4borg.highwire.dtl.DTLVardef@123a3e8org.highwire.dtl.DTLVardef@de0c52_HPS_FORMAT_FIGEXP M_TBL C_TBL

microbiology↗

bioRxiv2017

Could cyanobacteria have made the salinity transition during the late Archean?

Modern molecular evolutionary studies suggest the freshwater origin of cyanobacteria during the late Archean, about 2.7 Ga ago, with an even earlier evolution of oxidative photosynthesis. The large amount of oxygen required to oxygenate the Earths atmosphere during the Great Oxygenation Event (GOE) ~2.4 Ga is thought to have been produced by large cyanobacterial blooms in the open ocean. This then poses the question as to whether ancient lineages of cyanobacteria would have survived the salinity transition. This study investigates the effect of increasing salinity on the photosynthetic efficiency of two modern day descendants of ancient cyanobacteria, Chroococidiopsis thermalis PCC7203 and the root species, Gloeobacter violaceus PCC7421. Organisms were cultured in fresh, brackish or sea water analogous media under a present atmospheric level (PAL) atmosphere or an atmosphere with reduced O2 and elevated CO2 (rO2eCO2). The net photosynthesis (NP) rates were determined in liquid cultures, while the O2 and redox profiles were determined in pseudomats. While C. thermalis PCC7203 was able to grow under increasing salinities under both atmospheres tested, G. violaceus PCC7421 could not make the salinity change to sea water. NP rates were reduced for C. thermalis under increasing salinities, as were the levels of dissolved O2 in the media. A gene screen indicated that C. thermalis genome carries genes for both sucrose and trehalose synthesis, whereas G. violaceus has only the later genetic component, suggesting a mechanism for their differing salt tolerances. This study supports the hypothesis of Cyanobacterial evolution in freshwater environments and their transition into increasingly salty environments during the late Archaean, prior to the GOE.

microbiology↗

bioRxiv2017

Atmospheric CO2 availability does not equate to increased nodularin production in diazotrophic cyanobacteria, but does induce varying responses in net photosynthesis and N2 fixation rates.

Increasing levels of CO2 in the atmosphere are suggested to favour increased incidences of cyanobacterial blooms in water bodies, with a potential concomitant increase in toxin production. As nitrogen fixing cyanobacteria are independent of nitrate and ammonium, this pilot study investigated whether elevated atmospheric CO2 levels (eCO2), could increase toxin production and net photosynthesis (NP) rates in both terrestrial and aquatic diazotrophic cyanobacteria. Both toxin and non-toxin producing strains of Nostoc and Nodularia were grown at present atmospheric levels (PAL) of CO2 or near future elevated (eCO2) and net photosynthesis (NP) determined. Short term responses demonstrated CO2 associated increases and decreases in NP, with N. harveyana SAG44.85 showing little change in its NP at eCO2. Long term responses recorded increases in NP for all species in response to eCO2, except for N. harveyana on day 7. Nitrogen fixation rates were significantly higher by approx. 10 fold in the aquatic Nodularia species compared to the terrestrial Nostoc species tested. Moreover, nitrogen fixation rates were not significantly higher at eCO2, except for N. harveyana. There was no direct correlation between increased nodularin production and eCO2 in neither aquatic, nor terrestrial nodularin producing species, however there was a significant correlation between nodularin content and POC:PON ratio for the terrestrial Nostoc sp. 73.1 not observed for the aquatic Nodularia spumigena CCY9414.

ecology↗